Torque transmission differential for motor vehicles

ABSTRACT

The invention relates to a torque transmission differential for motor vehicles comprising a casing which is selectively rotated around an axis y-y′; a drive wheel axle with an axis Y-Y′; a gearing which is disposed inside the casing and which transmits the rotation movement from the case to the drive wheel axle; and a muzzle which is solidly connected to the casing and which is disposed between the gearing and the internal surface of the casing The gearing generally lies within an ellipsoid of rotation and the muzzle is more or less in the shape of an ellipsoid of revolution which is concentric to the gearing.

The present invention relates in a general manner to differentials forautomobiles and to a method for manufacturing a family of differentials.

More precisely, the invention relates in a first aspect to a torquetransmission differential for an automobile, this differential having acase selectively rotated around an axis Y-Y′, a drive wheel axle shaftwith axis Y-Y′, a gear train situated inside the case and whichtransmits the rotational movement of the case to the drive wheel axleshaft, and a muzzle joined with the case and interposed between the geartrain and the internal surface of the case, the gear train including apair of coaxial conical spider gears mounted on pins connected with thecase and having axis Z-Z′ perpendicular to axis Y-Y′, and a pair ofconical side gears having axis Y-Y′ which are joined to the drive wheelaxle shaft and which mesh with the spider gears, the gear traingenerally lying within an ellipsoid of revolution, and the muzzle havingthe general shape of an ellipsoid of revolution concentric with respectto the gear train.

Differentials of this type are known from the prior art. Muzzles inparticular have been used for more than ten years in differentials thattransmit low torques.

The capacity in terms of the torque that a differential is able totransmit is directly connected with the size of the ellipsoid withinwhich the gear train lies within. There are typically two differentialmodels: a first making it possible to transmit low torques and a secondmaking it possible to transmit high torques. According to prior art, thesize of the gear train is different for these two models, which alsoleads to different sizes for the case as well as for all of theaccessories: friction cups, spider gear pins etc. The means forproducing these elements must also be able to produce the two sizes.

In this context, the invention aims to reduce the costs connected withdifferentials by making certain elements common to the two differentialmodels.

For this purpose, and according to a first aspect, the invention relatesto a differential, which in other respects is in accordance with thegeneric definition given for it in the preamble above, essentiallycharacterized by the fact that the muzzle has at least a first pair ofshims.

In one possible embodiment, the muzzle consists of a thin shell havingthe shape of an ellipsoid of revolution, the shims of said first pairbeing situated on either the interior surface or exterior surface of thethin shell.

Advantageously, the shell can have the general shape of an ellipsoidalzone generated by revolution, having at least four circular openings,including two openings for passage of the pins of the spider gears andtwo openings for drive wheel axle shaft passage.

Preferably, the muzzle can have at least a second pair of shims, theshims of the first pair being roughly in the form of disks, eachcentered on an opening for passage of the pins of the spider gears andhaving in its center a cutout with the same diameter as thecorresponding opening, the shims of the second pair being roughly in theform of disks, each centered on an opening of the drive wheel axle shaftand having in its center a cutout with the same diameter as thecorresponding opening.

For example, the muzzle can have an interruption along a meridiansituated between two openings.

Advantageously, the muzzle can be a molded piece made of a syntheticmaterial such as polyamide.

Preferably, the first pair of shims has a diameter roughly equal to thediameter of the spider gears, and the second pair of shims has adiameter roughly equal to the diameter of the side gears.

In a second aspect, the invention relates to a method for manufacturinga family of torque transmission differentials, this family including atleast one differential model for transmitting a first, relatively lowertorque, and a second differential model for transmitting a second,relatively higher torque, this method comprising the steps consisting ofmanufacturing:

-   -   a first gear train, a first muzzle and a case for the first        differential model, and    -   a second gear train, a second muzzle and a case for the second        differential model, characterized by the fact that the case for        the first model is identical to the case for the second model,        and by the fact that the first and second muzzles are given, at        least locally, differing first and second respective        thicknesses, the first thickness being greater than the second.

Advantageously, it is possible for the first muzzle to have shims, andthe second muzzle not to have shims.

Preferably, the first muzzle can have first shims and the second muzzlecan have second shims, the thickness of the first shims being greaterthan that of the second shims.

Other characteristics and advantages of the invention will emerge moreclearly from the description given below, on an illustrative andnon-limiting basis, with reference to the appended drawings in which:

FIG. 1 is an oblique view of a differential according to the inventionin the assembled state, with the spider gear pins not represented.

FIG. 2 is a partial exploded view of the differential of FIG. 1,

FIG. 3 is an oblique view of the muzzle of FIG. 2, according to a firstembodiment,

FIG. 4 is a view of the muzzle of FIG. 2, according to a secondembodiment.

FIG. 5 is a partial exploded view of the two families of differentialsmanufactured with the process according to the invention.

As shown in FIG. 1, the invention relates to a torque transmissiondifferential for automobiles, this differential having case 10selectively rotated around an axis Y-Y′, drive wheel axle shaft 20 withaxis Y-Y′, gear train 30 situated inside case 10, and muzzle 40.

Gear train 30 transmits the rotational movement of case 10 to drivewheel axle shaft 20. Muzzle 40 is joined with case 10 and is interposedbetween gear train 30 and internal surface 12 of case 10 so as to reducefriction between gear train 30 and this internal surface 12.

Gear train 30 is of the epicycloidal type and has a pair of coaxialconical spider gears 32 mounted on pins 34 connected with case 10, and apair of conical side gears 36 with axis Y-Y′ which are joined to drivewheel axle shaft 20 and which mesh with spider gears 32. Axis Z-Z′ isperpendicular to axis Y-Y′.

Gear train 30 generally lies within an ellipsoid, typically a sphere,generated by revolution around a large axis Z-Z′ and having small axisY-Y′. Muzzle 40 has the general form of an ellipsoid corresponding tothe shape of gear train 30 and enveloping it in a concentric manner.

According to the invention, case 10 has the general shape of a bell withaxis Y-Y′, having base 14, which is selectively rotated by a deviceoutside of the invention that is not described, and bell-shaped part 16.

Base 14 has the shape of a disk with axis Y-Y′. Bell-shaped part 16 is apiece, generated by revolution around axis Y-Y′, that is flanged ontobase 14.

Drive wheel axle shaft 20 has two coaxial shaft halves 22 and 24. Shafthalf 22 is engaged in opening 22 a situated in the center of base 14 andis joined to one gear of the pair of side gears 36 situated insidebell-shaped part 16. Shaft half 24 is engaged in opening 24 a situatedat the summit of bell-shaped part 16, and is joined to the other gear ofthe pair of side gears 36 situated inside bell-shaped part 16.

Bell-shaped part 16 also has two other openings 19 situated on axisZ-Z′. Pins 34 for spider gears 32 comprise a single shaft passingthrough bell-shaped part 16. Shaft 34 is attached by one of its ends inone of openings 19, and by its opposite end in the other opening 19situated on the other side of bell-shaped part 16.

Spider gears 32 are mounted so as to rotate freely on this shaft 34, andeach engages the two side gears 36 by two diametrically opposed points32 a and 32 b.

Muzzle 40 consists of thin shell 44 and two pairs of shims 42 and 50.Thin shell 44 has the form of a zone of an ellipsoid generated byrevolution around a large axis Z-Z′ and having small axis Y-Y′, thiszone being delimited by two planes which are parallel to plane P formedby axes Z-Z′ and Y-Y′ and symmetrical with respect to this plane.

Thin shell 44 has at least four circular openings, including twoopenings 46 for passage of the pins and two openings 48 for passage ofthe drive wheel axle shaft.

Muzzle 40 has two pairs of shims, the shims of the first pair 42 beingin the form of disks, each centered on an opening 46 for passage of thepins and having in its center a cutout with the same diameter as thecorresponding opening, the shims of the second pair 50 being roughly inthe form of disks, each centered on an opening 48 for passage of thedrive wheel axle shaft and having in its center a cutout with the samediameter as the corresponding opening.

The first pair of shims 42 has a diameter roughly equal to the diameterof spider gears 32. The second pair of shims 50 has a diameter roughlyequal to the diameter of side gears 36.

In a first embodiment of the invention illustrated in FIG. 3, the firstand second pairs of shims 42 and 50 are situated on an exterior [sic;interior] surface of thin shell 44.

In a second embodiment of the invention illustrated in FIG. 4, the firstand second pairs of shims 42 and 50 are situated on an interior [sic;exterior] surface of thin shell 44.

Muzzle 40 has an interruption along a meridian situated between twoopenings, opening 46 for passage of the pins and opening 48 for passageof the wheel axle shaft.

Muzzle 40 is a molded piece made of synthetic material, typically apolymer such as polyamide.

According to a second aspect, the invention relates to a method formanufacturing a family of torque transmission differentials, this familyhaving at least a first differential model for transmitting a firstrelatively lower torque, and a second differential model fortransmitting a second relatively higher torque.

This method includes the steps consisting of manufacturing:

-   -   first gear train 301, first muzzle 401 and case 101 for the        first differential model, and    -   second gear train 302, second muzzle 402 and case 102 for the        second differential model.

According to the invention, case 101 for the first model is identical tocase 102, as shown in FIG. 5.

First muzzle 401 has first shims, second muzzle 402 has second shims,the thickness of the first shims being greater than the thickness of thesecond shims.

The second shims compensate exactly for the clearance left between geartrain 302 and the internal surface of case 101/102.

Since the size of first gear train 301 is smaller than that of secondgear train 302 while the size of case 101/102 is kept constant, it isnecessary to increase the thickness of the first shims in order tocontinue to compensate for the clearance with internal surface 12.

In another embodiment illustrated in FIG. 5, first muzzle 401 has shims,and second muzzle 402 does not have shims, only thin shell 44 beinginterposed between gear train 302 and internal surface 12.

It is well understood that the invention enables the same case 10 to beused for transmitting different torques. Case 10 and its accessories canbe standardized, and this results in considerable gains with regard toproduction of these pieces (narrower range) and in the management ofparts.

1. A torque transmission differential for an automobile comprising acase selectively rotated around an axis Y-Y′, a drive wheel axle shafthaving axis Y-Y′, a gear train situated inside the case and whichtransmits the rotational movement of the case to the drive wheel axleshaft, and a muzzle joined with the case and interposed between the geartrain and an internal surface of the case, the gear train including apair of coaxial conical spider gears mounted on pins connected with thecase and having an axis Z-Z′ perpendicular to axis Y-Y′, and a pair ofconical side gears having an axis Y-Y′ which are joined to the drivewheel axle shaft and which mesh with spider gears the gear traingenerally lying within an ellipsoid of revolution, and the muzzle havinga general shape of an ellipsoidal zone generated by the revolution,concentric with respect to the gear train, wherein the muzzle has atleast a first pair of shim.
 2. The torque transmission differentialaccording to claim 1, wherein the muzzle comprises a thin shell havingan interior surface and an exterior surface, the thin shell having thegeneral shape of an ellipsoidal zone generated by the revolution, saidfirst pair of shims being situated either on the interior surface or onthe exterior surface of the thin shell.
 3. The torque transmissiondifferential according to claim 2, wherein the thin shell has at leastfour circular openings, including two openings for passage of the pinsand two openings for passage of the drive wheel axle shaft.
 4. Thetorque transmission differential according to claim 3, wherein themuzzle has at least a second pair of shims, the first pair of shimsbeing roughly in the form of disks, each shin centered on an opening forpassage of the pins and having in its center a cutout with the samediameter as the corresponding opening, the second pair of shims beingroughly in the form of disks, each shim centered on an opening for thedrive wheel axle shaft and having in its center a cutout with the samediameter as the corresponding opening.
 5. The torque transmissiondifferential according to claim 1, wherein the muzzle has aninterruption along a meridian situated between two openings.
 6. Thetorque transmission differential according to claim 1, wherein themuzzle is a molded piece made of a synthetic material.
 7. The torquetransmission differential according to claim 4, wherein the first pairof shims has a diameter roughly equal to the diameter of the spidergears, and the second pair of shims has a diameter roughly equal to thediameter of the side gears.
 8. A method of manufacturing a family oftorque transmission differentials including at least one firstdifferential model for transmitting a first relatively lower torque anda second differential model for transmitting a second relatively highertorque, including manufacturing: a first gear train, a first muzzle anda case for the first differential model, and a second gear train, asecond muzzle and a case for the second differential model, wherein thecase for the first model is identical to the case for the second model,and the first and second muzzles have differing first and secondrespective thicknesses, the first thickness being greater than thesecond thickness.
 9. The process of manufacturing according to claim 8,wherein the first muzzle has shims, and the second muzzle does not haveshims.
 10. The process of manufacturing according to claim 8, whereinthe first muzzle has first shims having a thickness, the second muzzlehas second shims having a thickness, and the thickness of the firstshims is greater than the thickness of the second shims.
 11. The torquetransmission differential of claim 6, wherein the synthetic materialcomprises a polyamide.